NITROUS OXIDE INHALATION DOES NOT INFLUENCE PLASMA CONCENTRATIONS OF (3-ENDORPHIN OR MET-ENKEPHALIN-LIKE IMMUNOREACTIVITY

The possibility that nitrous oxide releases endogenous opioidpeptides into the circulation has been tested in 10 pain-free,unstressed volunteers breathing 30% nitrous oxide in oxygen.Despite achieving plateau concentrations in venous blood, accompaniedby subjective effects, there were no significant changes inplasma concentrations of immunoreactive ß-endorphin,methionine-enkephalin or ACTH. These results indicate that,in the absence of nociceptive input, the effects of the inhalationof nitrous oxide are unrelated to alterations in peripheralconcentrations of these endogenous opioid peptides. ^*Present address: Hospital for Sick Children, Melbourne, Australia.